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Final drive


Urban Surfer

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Urban Surfer

I may be pulling my final drive off soon and sending it to Anton, and was wondering. Is it possible to change the gears to a lower gear ratio? I doubt that I'll ever push the old crate to 200 kmh again, and I do ride in traffic a lot( still alive!) so the lower gear ratio certainly would help.

Any one ever done this?

Thanks

 

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Try the final drive from an r1100 RTP. The police bikes had a different ratio of 31:11 civilian RT has 32:11. Lower top speed, but faster acceleration.

 

Your final drive ratio is stamped into the final drive housing.

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Fellow Canadian new to forum..who is Anton and what does he do to final drives??

 

This is his shop. I have no personal experience, but since no one had answered your post yet, I am chiming in. He has a reputation as an excellent mechanic, and lots of folks seem to send in final drives and transmissions, among other things, for him to rebuild and then post back to the owners. Others will chime in with personal experience I'm sure.

 

 

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A GS and an RS I think have the lower gear ratio as well. So the parts are available to do the swap.

 

Not so. The GS and R have a lower FD ratio, but the RS has the same higher ration as the RT, assuming you are talking about the 5-speed 1100 bikes. You could try an 850 FD which is even lower than the GS/R one (though maybe they are rare over the pond). FWIW I used to have an 850GS but the low gearing drove me mad; the engine was revving the same in top (5th) as my 1100RS does in 4th. Personally I love the standard gearing in the 1100RS; in the UK it's just about perfect.

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Trullion,

Thank you for clarifying, I could not remember if it was the R or the RS that had the other low FD ratio.

 

My bad.

 

850 Fds are rare most places I believe.

I have not ridden one, but I can imagine that they would be TOO low.

It would really depend on what type of riding one plans on doing and the average speeds one travels at.

 

If all one like to do is OFF road riding or canyon carving, then the low gearing would be great, more low end grunt and crisper acceleration. If one is slabbing it on the interstates the RT tall gearing is better.

 

Many people I have read about including one VERY anal and thorough engineering type of guy on ADVrider did all kinds of calculating including wind drag coefficients and engine RPMs, top speeds......everything and found that the 1100RT 5 speed trans and FD were the most effiecient for optimizing power and top speed. The gearing on them keeps the motor in the power and able to get max rpms at top speed out of the motor rather than making it fall off at the top.

 

Interesting read. Not saying one is better than another...but for his research and useage it was the best.

 

I like my top end gearing but REALLY wish 1st was lower, very doggy off the line and tough on the clutch IMHO. Especially since I am heading toward making the RT a GS bike now....I may be looking for a GS/R FD eventually.

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...

 

Many people I have read about including one VERY anal and thorough engineering type of guy on ADVrider did all kinds of calculating including wind drag coefficients and engine RPMs, top speeds......everything and found that the 1100RT 5 speed trans and FD were the most effiecient for optimizing power and top speed. The gearing on them keeps the motor in the power and able to get max rpms at top speed out of the motor rather than making it fall off at the top.

 

Interesting read. Not saying one is better than another...but for his research and useage it was the best.

 

...

 

I don't know if you were thinking of this thread and post: R1150RT Top Speed but I came to the same conclusion after looking at drag and gearing that the R1100RT was well geared to its top horsepower.

 

The other thing that will happen if you were to change the final drive gearing toward more reduction in the drive would be a small reduction in fuel economy.

 

I found that by adding a Wideband O2 sensor and richening the mixture of the 1150 I have much better pull at lower RPMs and did some torque tests to convince myself. Adding the Wideband O2 isn't too bad a project but if you keep an eye on the O2 thread, it might be that you could richen the effect of stock O2 sensor a bit but I'm a month or two away from knowing whether that's the case.

 

RB

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Roger,

That is the thread I was thinking of. I thought it was on ADV, wrong again...I am batting 1000 on flubs today.

 

Would lowering the gear ratio increase fuel economy....as long as you were not riding slab much?

 

I mean if all you did was city riding, or fire road stuff and almost no 70+ mph cruising you would possibly get better mileage with the lower gearing. Of course not so if you slab alot then you want tall gearing to drop RPMs at hiway speeds...

 

Still batting 1000 or get I get one right today?

Havin a rough day. lol

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Urban Surfer

Interesting response, thanks fellas. I think if the final drive has to come apart, reducing the gearing would be the answer rather than tinkering with the fuel system.

I changed the rear diff in a pickup years ago and it really transformed the truck.

I'll talk to Anton

Thanks

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Interesting response, thanks fellas. I think if the final drive has to come apart, reducing the gearing would be the answer rather than tinkering with the fuel system.

I changed the rear diff in a pickup years ago and it really transformed the truck.

I'll talk to Anton

Thanks

 

The best part of what you're proposing is that for every rpm and gear you'll get more rear wheel torque. Changing from 2.82 to 2.91 would get you 3% more, if that matters.

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Roger,

That is the thread I was thinking of. I thought it was on ADV, wrong again...I am batting 1000 on flubs today.

 

Would lowering the gear ratio increase fuel economy....as long as you were not riding slab much?

 

I mean if all you did was city riding, or fire road stuff and almost no 70+ mph cruising you would possibly get better mileage with the lower gearing. Of course not so if you slab alot then you want tall gearing to drop RPMs at hiway speeds...

 

Still batting 1000 or get I get one right today?

Havin a rough day. lol

 

At high speeds the losses are mainly from aerodynamic drag. At low speeds with high manifold vacuum, pumping losses are high. Specific fuel consumption can go from 0.5 lbs/HP/hr when the throttle is open to two or three times that when the throttle is only open a few degrees. As a result of that the mileage will be a bit worse all the time, even at low speeds.

 

Another way to think of it is that every speed takes a certain HP. If you pick a high gear with low RPMs then you have to open the throttle more and the engine is more efficient with fuel. If you pick a low gear (or FD ratio) then the RPMs go up, torque at the engine goes down and the manifold vacuum goes up.

 

Although I understand the thinking on the higher FD ratio, strengthening the fueling is a better bang for the buck.

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SAAB93driver

I changed out my R1150RS FD for a 3.0 a very long time ago, it's much happier starting out when fully loaded in first and cruising on the highway. It was geared too tall IMO and the 6th gear was virtually useless unless I was going 85 or 90. A better fix would have been the close ratio gearbox BMW had for some applications but the FD swap was much less evasive and gave satisfactory results for me.

 

This old summary I did might help

 

R1150RS 6-speed gearbox ratios with the internal reduction of 1.9:1 included in the gearbox output ratio:

 

FD 2.82 2.91 3.0 3.20 3.36

from 1150RS 1150RT 1100R 850RT 850R

Gear/overall

1st 3.895 / 10.983 11.334 11.682 12.464 13.087

2nd 3.04 / 8.572 8.846 9.12 9.728 10.214

3rd 2.413 / 6.804 7.022 7.239 7.721 8.107

4th 1.9722/ 5.561 5.739 5.916 6.311 6.626

5th 1.71 / 4.822 4.976 5.130 5.472 5.745

6th 1.33 / 3.750 3.870 3.990 4.256 4.468

 

For comparison stock 1100RS 2.818:1 FD

 

gear/overall

1st 4.163 / 11.731

2nd 2.914 / 8.212

3rd 2.133 / 6.01

4th 1.740 / 4.90

5th 1.450 / 4.086

 

So depending upon what you want - Overdrive with more flexibility than stock or top speed comparable to 1100RS it looks like the 2.91 from the 1150 RT or the 3.0 from the 1100R might be the solution, respectively. I know someone on here has fitted the 3.0 and is happy with it but don't recall whom.

 

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Urban Surfer
I changed out my R1150RS FD for a 3.0 a very long time ago, it's much happier starting out when fully loaded in first and cruising on the highway. It was geared too tall IMO and the 6th gear was virtually useless unless I was going 85 or 90. A better fix would have been the close ratio gearbox BMW had for some applications but the FD swap was much less evasive and gave satisfactory results for me.

 

This old summary I did might help

 

R1150RS 6-speed gearbox ratios with the internal reduction of 1.9:1 included in the gearbox output ratio:

 

FD 2.82 2.91 3.0 3.20 3.36

from 1150RS 1150RT 1100R 850RT 850R

Gear/overall

1st 3.895 / 10.983 11.334 11.682 12.464 13.087

2nd 3.04 / 8.572 8.846 9.12 9.728 10.214

3rd 2.413 / 6.804 7.022 7.239 7.721 8.107

4th 1.9722/ 5.561 5.739 5.916 6.311 6.626

5th 1.71 / 4.822 4.976 5.130 5.472 5.745

6th 1.33 / 3.750 3.870 3.990 4.256 4.468

 

For comparison stock 1100RS 2.818:1 FD

 

gear/overall

1st 4.163 / 11.731

2nd 2.914 / 8.212

3rd 2.133 / 6.01

4th 1.740 / 4.90

5th 1.450 / 4.086

 

So depending upon what you want - Overdrive with more flexibility than stock or top speed comparable to 1100RS it looks like the 2.91 from the 1150 RT or the 3.0 from the 1100R might be the solution, respectively. I know someone on here has fitted the 3.0 and is happy with it but don't recall whom.

 

Thanks for that! I was only considering re gearing the final drive because I believe it is in need of repair. I don't fix things unless they are broke, and while it is apart why not.

Tinkering with the fuel system is much cheaper, but it's all working fine for now.

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I changed out my R1150RS FD for a 3.0 a very long time ago, it's much happier starting out when fully loaded in first and cruising on the highway. It was geared too tall IMO and the 6th gear was virtually useless unless I was going 85 or 90. A better fix would have been the close ratio gearbox BMW had for some applications but the FD swap was much less evasive and gave satisfactory results for me.

 

This old summary I did might help

 

R1150RS 6-speed gearbox ratios with the internal reduction of 1.9:1 included in the gearbox output ratio:

 

FD 2.82 2.91 3.0 3.20 3.36

from 1150RS 1150RT 1100R 850RT 850R

Gear/overall

1st 3.895 / 10.983 11.334 11.682 12.464 13.087

2nd 3.04 / 8.572 8.846 9.12 9.728 10.214

3rd 2.413 / 6.804 7.022 7.239 7.721 8.107

4th 1.9722/ 5.561 5.739 5.916 6.311 6.626

5th 1.71 / 4.822 4.976 5.130 5.472 5.745

6th 1.33 / 3.750 3.870 3.990 4.256 4.468

 

For comparison stock 1100RS 2.818:1 FD

 

gear/overall

1st 4.163 / 11.731

2nd 2.914 / 8.212

3rd 2.133 / 6.01

4th 1.740 / 4.90

5th 1.450 / 4.086

 

So depending upon what you want - Overdrive with more flexibility than stock or top speed comparable to 1100RS it looks like the 2.91 from the 1150 RT or the 3.0 from the 1100R might be the solution, respectively. I know someone on here has fitted the 3.0 and is happy with it but don't recall whom.

 

I think your R1150RT numbers aren't quite right. Here's what I have from Clymers and BMW.

 

R1150RT

 

1st - 3.683

2nd - 3.022

3rd- 2.393

4th - 1.961

5th - 1.700

6th - 1.316

 

FD 2.91:1

 

Overall

1st 10.71753

2nd 8.79402

3rd 6.96363

4th 5.70651

5th 4.947

6th 3.82956

 

So if you shift the FD from 2.91 to

 

3.0 you add 3% to the torque and drop the speed in each gear by the same

3.2 adds 10%

3.26 adds 15%

 

With the slight adjustment I've made to the mixture I can cruise in 6th gear at 45 MPH on level ground (not that I do). By 55 MPH 6th gear is pretty responsive.

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Urban Surfer
I changed out my R1150RS FD for a 3.0 a very long time ago, it's much happier starting out when fully loaded in first and cruising on the highway. It was geared too tall IMO and the 6th gear was virtually useless unless I was going 85 or 90. A better fix would have been the close ratio gearbox BMW had for some applications but the FD swap was much less evasive and gave satisfactory results for me.

 

This old summary I did might help

 

R1150RS 6-speed gearbox ratios with the internal reduction of 1.9:1 included in the gearbox output ratio:

 

FD 2.82 2.91 3.0 3.20 3.36

from 1150RS 1150RT 1100R 850RT 850R

Gear/overall

1st 3.895 / 10.983 11.334 11.682 12.464 13.087

2nd 3.04 / 8.572 8.846 9.12 9.728 10.214

3rd 2.413 / 6.804 7.022 7.239 7.721 8.107

4th 1.9722/ 5.561 5.739 5.916 6.311 6.626

5th 1.71 / 4.822 4.976 5.130 5.472 5.745

6th 1.33 / 3.750 3.870 3.990 4.256 4.468

 

For comparison stock 1100RS 2.818:1 FD

 

gear/overall

1st 4.163 / 11.731

2nd 2.914 / 8.212

3rd 2.133 / 6.01

4th 1.740 / 4.90

5th 1.450 / 4.086

 

So depending upon what you want - Overdrive with more flexibility than stock or top speed comparable to 1100RS it looks like the 2.91 from the 1150 RT or the 3.0 from the 1100R might be the solution, respectively. I know someone on here has fitted the 3.0 and is happy with it but don't recall whom.

 

I think your R1150RT numbers aren't quite right. Here's what I have from Clymers and BMW.

 

R1150RT

 

1st - 3.683

2nd - 3.022

3rd- 2.393

4th - 1.961

5th - 1.700

6th - 1.316

 

FD 2.91:1

 

Overall

1st 10.71753

2nd 8.79402

3rd 6.96363

4th 5.70651

5th 4.947

6th 3.82956

 

So if you shift the FD from 2.91 to

 

3.0 you add 3% to the torque and drop the speed in each gear by the same

3.2 adds 10%

3.26 adds 15%

 

With the slight adjustment I've made to the mixture I can cruise in 6th gear at 45 MPH on level ground (not that I do). By 55 MPH 6th gear is pretty responsive.

 

That sounds like a good idea. I may as well fix both

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Evening Urban Surfer

 

It is a LOT more expensive to buy a new gear set then (have someone) set the gear lash up correctly than it is to just buy a GS, RT-P, or R final drive with a better gear ratio already in it.

 

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